1. Is the MySQL service perhaps still installed from WAMP? Don't know. How do I find out? Whilst I have WAMP installed, it was not running when I tried to start MySQL from the XAMPP Control Panel. Do I need to uninstall WAMP?

2. What's in the \xampp\mysql\data\mysql_error.log??? Interestingly, that file is not there and not in any of the folders in XAMPP. Why?

I read in the XAMPP FAQ that I need to disable the User Account Control (UAC), or use the program "msconfig", then restart Windows. Would disabling the UAC not cause my computer to be expose to security risk? Could this be the source of my difficulty?

A - yes. you should probably un-install WAMP if you plan to use XAMPP - they are redundant BUT - you should un-install any items you had running as Service FIRST - i.e. htppd.exe (Apache) and MySQL (that's a WAMP thingy, so I don't know where they handle that, I haven't used it in a long time )

how to check for MySQL as service (or Apache):

Computer > Manage > Services

Look for MySQL or mysql - right clcik to get its properties, then look at 'path to exectable' if it show it in WAMP's folder that is proabably the issue or Apache 2.2 or httpd.exe

B - the UAC issue is circumvented by using 'Run as Administrator' AFAIK. I don't normally work on Vista machine, but I'll check. There is another workaround that obviates all that - when you run XAMPP to develop on - use the administrator account.

Use the CMD prompt with 'run as administrator' then type 'net user administrator /active:yes'